This invention relates to a fuel delivery rail assembly for an internal combustion engine, especially for an automotive engine, equipped with a fuel injection system. The fuel delivery rail assembly delivers pressurized fuel supplied from a fuel pump toward intake passages or chambers via associated fuel injectors. The assembly is used to simplify installation of the fuel injectors and the fuel supply passages on the engine.
An example of a fuel delivery rail assembly having a rectangular section is shown in FIG. 5 of the drawings. In this assembly, an elongated conduct 71 is formed by a steel tube having a rectangular hollow section. To an end of the conduit 71, a fuel inlet pipe 77 for introducing gasoline fuel is secured, and to the other end of the conduit 71, a fuel return pipe 78 leading to an exit for residual fuel is secured, both pipes being welded to the conduit 71 by copper brazing. To the insides of the conduit 71 and the pipes 77, 78, a copper plating is coated for protecting the surfaces from rust and for keeping the fuel clean. At the intermediate portion of the conduit 71, four tubular sockets 74 are inserted into guide holes arranged within the bottom wall of the conduit 71 at predetermined intervals, and welded thereto by copper brazing. These sockets 74 are so formed as to receive associated tips of fuel injectors. The axial directions of the sockets should precisely line up in alignment with the respective axial direction of the injectors. Furthermore, pitch lengths between adjacent sockets should precisely coincide with the corresponding pitch lengths between associated injectors. One of the objects of the present invention is directed to these alignment problems as discussed in detail below.
On the aforementioned copper plating portions, a further coating is needed for preventing copper ion from dissolving in the fuel. Therefore, after the copper brazing and coating, a chemical plating (non-electrolytic plating) is applied to the all surfaces by coating thin metallic layers such as Ni-P or Sn. However, since the assembly is formed in a box shape, it takes a considerable time to let the plating liquid flow into the conduit and then drain away the conduit perfectly. Furthermore, a rotating action and an up and down action of the conduit are needed for draining residual air and liquid during the plating steps. Even if these actions are performed, it is difficult to eliminate plating defects caused by the remaining air and liquid. As a result, undesirable rust is generated from the plating defects. After the treatment, the residual plating liquid staying at the inside of the box-shape conduit is carried back to a container for renewal, whereby a liquid degradation and consumption are accelerated, resulting in an increase of plating liquid supply or recirculation steps.
Referring to the sockets 74, especially interior surfaces thereof should be smoothly finished in order to establish a fluid tight seal of an O-ring after accommodating the respective fuel injector. In manufacturing process of the metallic socket 74, many kinds of working steps are needed. For example, at first a rough fabrication is made by a forging work, and then it is machined to make a form, of the interior surface. Finally, the socket is finished with a burnishing machine until the predetermined smoothness is obtained. For making the socket 74, abovementioned many kinds of time-consuming working steps and transferring handlings are needed, resulting in an increase of manufacturing cost.
Furthermore, it has been found that this kind of fuel delivery rail assembly generates a special noise due to a vibration of itself caused by the associated engine.
In Japanese utility model public disclosure No. 107050/1984, there is disclosed a combined type fuel delivery rail assembly which comprises a conduit made from extruded aluminum material, and sockets and brackets made from other materials. However, the connected portion between the conduit and the socket tends to be separated therefrom, thereby causing a fuel leakage or breakdown.